In an angle detection apparatus of a rotary shaft of a motor or the like, a resolver is used for angle detection. The resolver receives an excitation signal, and generates signals by amplitude-modulating the excitation signal in accordance with a rotation angle.
Two angle signals (i.e. a SIN Φ component and a COS Φ component of an angle) outputted by the resolver may have a phase shift due to influence of a signal delay in propagation from the resolver to digital conversion. The occurrence of the phase shift leads to the problem of deterioration in accuracy of angle detection of the rotary shaft. Also, the occurrence of a change in amplitude leads to the problem of the deterioration in the accuracy of the angle detection of the rotary shaft.